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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Got the same issue. In my case it was because I was overwriting Array.prototype.flat.
Even though it says it's using node8 and flat was introduced in v11, it still a had problem with that somehow. So avoid overwriting any build-in objects.